A number of ophthalmic surgical procedures performed on a patient's retina require illuminating the retina with a light spot. Some exemplary procedures include a vitrectomy, macula hole surgery, retinal detachment surgery, and diabetic retinopathy surgery. In one ophthalmic surgical procedure, typically referred to as retinal photocoagulation, a laser light spot is directed to a selected portion of a patient's retina to deposit energy, thereby causing coagulation of the local tissue. Such a photocoagulation procedure can be employed, for example, to seal leaky blood vessels, destroy abnormal blood vessels, or seal retinal tears. For such procedures, the surgeon performing the procedure must be able to not only properly observe the site and its surroundings during the procedure, but must be able to do so safely, without fear of harm to his or her own retina from the reflected illumination light spot.
For these and other ophthalmic procedures a surgeon will typically employ a light source, such as a high brightness xenon illumination source, to illuminate a surgical site and allow him or her to clearly see the area of surgical interest. Such light sources, however, project light comprising multiple wavelengths, including violet and ultra-violet wavelengths that have been found to be harmful to human retinas. In such cases, it is not only the patient's eyes that must be protected from the harmful wavelength radiation, but also the observing surgeon's eyes.
To minimize the risk to a surgeon's eyes, optical safety filters are extensively used in many types of direct-vision optical systems to protect the eyes of a user from damage by reflected light radiation, such as laser and other illumination light radiation, and also to protect the patient from harmful direct illuminating light radiation. One type of system in which such filters are used is a laser surgery system, such as for performing the procedures described above, which can deliver laser and illumination light source radiation to a surgical site on a patient for tissue ablation, artery incision, etc., while permitting a surgeon performing the procedure to observe the surgical site.
ISO Standard 15752 describes hazards to the retina associated with absorption of certain ultra-violet (“UV”) and near-UV wavelengths, specifically those wavelengths below 420 nm. It is an accepted safety precaution to filter ophthalmic illumination sources to prevent the transmission of these UV and near-UV wavelength radiation to lower the risk of harm to the retinas of an observing surgeon and/or a patient. However, filtering UV radiation from an illumination source results in filtered light having a tint that is not color-neutral, but is instead, for example, a bright yellow color. Bright yellow (or other colored) illumination of a surgical site can disrupt a surgeon's color perception. For a surgeon using a filtered illumination light, UV filtration resulting in a pronounced transmission color will make it difficult for the surgeon to properly assess the conditions at the surgical site. As a result, surgeon comfort, efficiency, and, ultimately, the quality of the surgical result, can be compromised.
Therefore, a need exists for a color-compensating retinal safety filter for use in a surgical illuminator that can reduce or eliminate the coloration and other problems associated with prior art optical safety filters.